Raman scattering is used to investigate the room temperature phonons of tetragonal $(I4∕m)$ ${\mathrm{Sr}}_2\mathrm{Co}\mathrm{W}{\mathrm{O}}_6$ and monoclinic $(P{2}_1∕n)$ ${\mathrm{Ca}}_2\mathrm{Co}\mathrm{W}{\mathrm{O}}_6$ , ${\mathrm{Sr}}_2\mathrm{Co}\mathrm{Te}{\mathrm{O}}_6$ , and ${\mathrm{Ca}}_2\mathrm{Co}\mathrm{Te}{\mathrm{O}}_6$ double perovskites. Both tetragonal and monoclinic structures result from small distortions of the $Fm\overline{3}m$ cubic lattice. Therefore, phonons were assigned according to correlations with those observed in the prototype $A_2{B}^{\prime }{B}^{″}{\mathrm{O}}_6$ $Fm\overline{3}m$ cubic structure and the internal vibrational modes of the oxygen octahedra. The observed shifts of some vibrations in the $A_2\mathrm{Co}B{\mathrm{O}}_6$ compounds upon changing either $A$ or $B$ elements are tentatively explained.

In this paper we present a Raman-scattering study of the phase transitions in the ${\mathrm{PbZr}}_{1-x}{\mathrm{Ti}}_x{\mathrm{O}}_3$ systems around the morphotropic phase boundary over a wide temperature range. The boundary between rhombohedral and monoclinic phases was found to be a quasivertical line between $x=0.46\mathrm{}$ and $x=\mathrm{0.47.}\mathrm{}$ We also studied the monoclinic-tetragonal phase boundary and our spectroscopic results agree very well with those reported by using x-ray diffraction.

Polarized Raman spectroscopy has been used to obtain the room-temperature phonon spectra of the series of rare earth orthovanadate single crystals: $\mathrm{Sm}\mathrm{V}{\mathrm{O}}_4$ , $\mathrm{Ho}\mathrm{V}{\mathrm{O}}_4$ , $\mathrm{Yb}\mathrm{V}{\mathrm{O}}_4$ , and $\mathrm{Lu}\mathrm{V}{\mathrm{O}}_4$ . The observed Raman frequencies follow the overall mode distribution expected for ${\mathrm{REVO}}_4$ compounds with the tetragonal zircon structure. The variation of the mode frequency with atomic number across the lanthanide orthovanadate series was investigated, and the trend exhibited by the internal modes was explained by considering the force constants of $\mathrm{V}{\mathrm{O}}_4$ tetrahedron.